Field of the Invention
The present invention lies in the field of semiconductors. Specifically, the invention relates to a process for producing a light-emitting and/or light-receiving semiconductor body having at least one semiconductor layer composed of GaAsxP1xe2x88x92x, where 0xe2x89xa6x less than 1.
Light-emitting diodes with semiconductor bodies of that type are known in the art. For instance, European patent application EP 584 599, describes a light-emitting diode chip in which an n-conducting GaP epitaxial layer is applied to an n-conducting GaP substrate and a p-conducting GaP epitaxial layer is applied to the n-conducting GaP epitaxial layer. The underside of the GaP substrate is provided with a contact metalization layer made of an Auxe2x80x94Ge alloy and a contact metalization layer is applied to the top side of the p-conducting GaP epitaxial layer. The latter contact metalization layer is composed, proceeding from the p-conducting GaP epitaxial layer, for example, of an Au layer, an Auxe2x80x94Zn layer, a Tixe2x80x94Wxe2x80x94N layer, and an Au or Al layer.
Furthermore, light-emitting diodes are known in which a layer sequence made of GaAsP is applied to a GaP substrate by means of epitaxy. That layer sequence has, for example, proceeding from the GaP substrate, first of all a GaAsP transition layer with an increasing As content, an n-doped GaAsP layer (dopant: e.g. tellurium or sulfur) and a p-doped GaAsP layer (dopant: zinc). A contact metalization layer is applied to the p-doped GaAsP layer. The metalization layer comprises, for example, proceeding from the p-doped GaAsP layer, a gold-zinc layer, a TiWN layer and an aluminum layer. The underside of the GaP substrate is provided with a contact metalization layer comprising, for example, a gold-germanium layer applied to the GaP substrate.
Depending on the As content, a light-emitting diode which emits light from the yellow up to super red region can be produced using a semiconductor body described above. However, the disadvantage of these semiconductor bodies is that only a fraction of the light generated in the semiconductor body is coupled out from the semiconductor body.
U.S. Pat. No. 4,582,952 describes a solar cell which, proceeding from a transparent GaP substrate, is constructed from a first p-doped GaAsP layer having a gradated As content, a second p-doped GaAsP layer, an n-doped GaAsP layer and a GaP covering layer. The GaP substrate and the GaP covering layer are each provided with a plurality of metal contacts.
The efficiency of a light-emitting diode or of a photodiode or solar cell is determined to an appreciable extent by the losses occurring when the radiation exits from or enters into the semiconductor body. A primary cause of these losses is the considerable difference between the refractive indices of the semiconductor material and the adjoining medium (for example air or plastic encapsulation). The large difference has the effect that a very small critical angle of total reflection for the passage of radiation through the surface of the semiconductor body exists. The proportion of radiation which exits directly from the semiconductor body, however, is only that proportion which is incident on the interface at a smaller angle with respect to the normal to the surface than the critical angle. The remaining proportion of the radiation is reflected back into the semiconductor body.
It is accordingly an object of the invention to provide a process for producing a light-emitting and/or receiving semiconductor body having at least one semiconductor layer made of GaAsxP1xe2x88x92x, where 0xe2x89xa6x less than 1, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which exhibits improved output coupling and/or input coupling of light as compared with the prior art.
With the foregoing and other objects in view there is provided, in accordance with the invention, a process for producing a light-emitting and/or light-receiving semiconductor body with at least one semiconductor layer composed of GaAsxP1xe2x88x92x, where 0xe2x89xa6x less than 1. The method comprises:
treating at least a part of a surface of the semiconductor layer in a first etching step with an etching solution having the composition H2SO4:H2O2:H2O and in a second etching step with hydrofluoric acid, for producing a roughness on the surface of the semiconductor layer.
In accordance with an added feature of the invention, the roughness resulting from the two etching steps is a multiplicity of mutually adjacent sawteeth formed in the surface of the semiconductor layer.
In other words, at least a portion of the surface of the semiconductor layer is treated with an etching solution (H2SO4:H2O2:H2O) and then with dilute hydrofluoric acid. This results in a roughness on the treated part of the surface of the semiconductor layer.
The advantageous effect achieved by the roughness of the surface is that, in comparison with a planar surface, a larger proportion of the radiation generated in the semiconductor body impinges on the surface of the semiconductor layer at an angle which is smaller than the critical angle of total reflection.
A further advantage of the roughened semiconductor surface is that, in the embodiment in which the semiconductor body is surrounded directly by a plastic encapsulation, increased adhesive strength between the semiconductor body and the plastic encapsulation is obtained. This reduces the risk of detachment of the plastic encapsulation from the semiconductor body during operation and consequently accelerated aging of the semiconductor component.
In accordance with another feature of the invention, a GaP semiconductor substrate is provided and a layer sequence with at least one nitrogen-doped GaP epitaxial layer is applied on the substrate. Alternatively, a layer sequence is applied with at least one GaAsxP1xe2x88x92x epitaxial layer, where 0 less than x less than 1.
In accordance with an additional feature of the invention, the treating step comprises forming the roughness on an entire free surface of the semiconductor body. In a semiconductor body having an n-doped GaP substrate on which a layer sequence made of GaAsP is applied, the entire free surface of the semiconductor body is roughened. In this case, free surface is to be understood to mean that partial region of the surface which is not provided with a contact metalization layer.
In the case of light-emitting diodes having such a semiconductor body which is suitable for the generation of light, the GaP substrate is transmissive for the electromagnetic radiation generated in the GaAsP layer sequence, since the energy gap of GaAsP is smaller than that of GaP. Therefore, the radiation can advantageously be coupled out from the semiconductor body through the entire free surface thereof.
With the above and other objects in view there is also provided, in accordance with the invention, a process for simultaneously producing a plurality of light-emitting and/or light-receiving semiconductor bodies having at least one semiconductor layer composed of a semiconductor material selected from the group consisting of GaAsxP1xe2x88x92x, where 0xe2x89xa6x less than 1, and GaP:N, the method which comprises:
forming a layer sequence of GaAsxP1xe2x88x92x, where 0xe2x89xa6x less than 1, on a GaP substrate wafer;
applying a first contact metalization to an underside of the substrate wafer and applying at least one second contact metalization to a top side of the layer sequence;
treating a free surface of the layer sequence with an etching solution having the composition H2SO4:H2O2:H2O in a first etching step and with hydrofluoric acid in a second etching step, for producing a roughness in the free surface; and
severing a semiconductor wafer comprising the substrate wafer, the layer sequence, the first contact metalization and the second contact metalization into individual semiconductor bodies.
In an alternative process of the invention, the following method steps are effected:
forming a layer sequence of GaAsxP1xe2x88x92x, where 0xe2x89xa6x less than 1, on a GaP substrate wafer;
applying a first contact metalization to an underside of the substrate wafer and applying a plurality of second contact metalizations to a top side of the layer sequence;
placing a semiconductor wafer comprising the substrate wafer, the layer sequence, the first contact metalization, and the second contact metalization on a carrier;
severing the semiconductor wafer into individual semiconductor bodies with free surfaces; and
treating the free surfaces of the semiconductor bodies with an etching solution having the composition H2SO4:H2O2:H2O in a first etching step and with hydrofluoric acid in a second etching step, for producing a roughness in the free surfaces.
It is advantageous for a contact metalization layer applied to an underside of the GaP substrate to have a reflecting surface at the boundary with the semiconductor body. The consequence of this is that the radiation emitted by the GaAsP layer sequence in the direction of the contact metalization layer is largely reflected from the latter and can subsequently be coupled out through the free surface.
In accordance with a further feature of the invention, the first etching step in all of the above alternatives comprises selecting a ratio of 3:1:1 for the etching solution H2SO4:H2O2:H2O, choosing a temperature of between 15 and 80xc2x0 C. and an etching duration of between 30 seconds and 10 minutes. Among other advantages, these process parameters render a semiconductor body surface completely free of contamination and other residues.
In accordance with a concomitant feature of the invention, the second etching step comprises etching with 40-50% hydrofluoric acid, at a temperature of between 15 and 30xc2x0 C. (preferably 25xc2x0), and for an etching duration of between 30 minutes and 120 minutes.
The resulting surface roughness attained with the two etching steps has the shape of sawteeth which are arranged next to one another and have a height of approximately 1 xcexcm. In the case of light-emitting diodes, a light increase of approximately 40% can advantageously be obtained as a result of this.
As noted above, in another preferred development of the novel process, the semiconductor body has a GaP substrate on which there is applied a layer sequence made of nitrogen(N)-doped GaP (in short: GaP:N). In the case of such a semiconductor body which is also suitable for the generation of light the substrate is advantageously transmissive for the radiation generated in the GaP layer sequence, with the result that in this case, too, a substantial increase in the output coupling of light is obtained by virtue of the roughness of the semiconductor surface.
In a particularly advantageous process for simultaneously producing a plurality of semiconductor bodies of the type mentioned in the introduction, a layer sequence made of GaAsxP1xe2x88x92x, where 0xe2x89xa6x less than 1, or GaP:N is firstly applied to a substrate wafer made of GaP. Afterwards, a first contact metalization layer is applied to the underside of the substrate wafer and a plurality of second contact metalization layers are applied to the top side of the layer sequence. Subsequently, the free surface of the layer sequence is firstly treated with the etching solution having the composition H2SO4:H2O2:H2O in a first etching step and with hydrofluoric acid (HF) in a second etching step.
Finally, the semiconductor wafer, comprising substrate wafer, layer sequence, first and second contact metalization layers, is separated to form individual semiconductor bodies, for example light-emitting diode chips.
If provision is made for the side areas of the semiconductor bodies to be roughened as well, then after the application of the first and second contact metalization layers, the semiconductor wafer is applied for example to an adhesive film or another carrier and separated into individual light-emitting diode semiconductor bodies. The two above-mentioned etching steps are subsequently carried out before the separated semiconductor bodies are then lifted off from the carrier and processed further to form light-emitting diodes, for example.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a process for producing a light-emitting and/or receiving semiconductor body, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.